This invention relates to a method of producing a compensating element, particularly to a method of producing a light source compensating element for scanners. The acquired light source compensating element can be arranged between the light-radiating device (the light source) of a scanner and the document text page (the scanned object) for compensating the light emitted from the light source, thereby forming specific (or even) brightness distribution of light projected onto the surface of the scanned object. The scanner configured with the light source compensating element is also disclosed.
A typical scanning apparatus comprises a light-radiating device for moving along a scanning path to illuminate an object or document (for example, a piece of paper or a transparency) and projecting the scanned image of the scanned object through a focusing device to a receiving device (such as a charge-coupled device (CCD), or a contact image sensor (CIS)). However, the brightness distribution of light emitted from the light-radiating device to the surface of the scanned object will become uneven due to the properties of the light source. Consequently, the image quality projected to the image receiving device will be degraded.
Please refer to FIG. 1. In a typical CIS scanner, the light-radiating device (light source) comprises an LED 10 with a light guide 12. The LED 10 emits light, which transmits along the light guide 12 and is projected onto the scanned object. The light brightness distribution onto the text page of the scanned object 14 is shown in FIG. 1. In FIG. 1, Imax and Imin represent the maximum and the minimum brightness, respectively, whereas Im is defined as
            I      max        +          I      min        2
to represent the average brightness. The unevenness of light brightness distribution is defined as                     I        max            -              I        m                    I      m        xc3x97  100  ⁢      %    .  
Currently, the unevenness of the light distribution on the surface of the scanned object may be resolved by configuring the geometric structure of the light guide 12 to make the light projected by the LED through the light guide more even (uniform). However, the result achieved is not always satisfactory. Another resolution is to first drive the light source in a CIS scanner to scan an even blank (white element). The scanned data then serves as a reference white. In later scanning of other documents, the scanned data of other documents will be compared with the corresponding value of the reference white to obtain image data approximate to the source documents. However, this method will reduce the image quality of the darker areas on the source documents.
Accordingly, an object of this invention is to provide a method of producing a light source compensating element for scanners. The light source compensating element fabricated in accordance with this invention can be arranged between the scanner light source (the light-radiating device) and the scanned object. Therefore, the light emitted from the light source passing through the light source compensating element has even (uniform) brightness distribution on the scanned object.
Another object of this invention is a method of producing light source compensating elements for scanners. The light emitted from the light source through the light source compensating element has a desired (predetermined and specific to user""s requirement) brightness distribution of light on the scanned object.
Yet another object of this invention is to provide an image scanning apparatus, characterized in that it comprises a light source compensating element for adjusting the brightness distribution of the light projected onto a scanned object. The light source compensating element is arranged between the light-radiating device and the scanned object, for enabling the light passing through the compensating element to have a specific (or even) brightness distribution on the scanned object.
To achieve the above object of projecting evenly distributed light onto the surface of a scanned object through a light source compensating element, this invention provides a method of producing a light source compensating element for scanners, comprising: providing an unexposed target film; projecting the light from the light source of the scanner to the target film and controlling the time of exposing the target film; and developing the exposed target film to obtain low transmittance distribution on the target film corresponding to the higher brightness distribution of the light used to expose the target film and high transmittance distribution on the target film corresponding to the lower brightness distribution of the light used to expose the target film. The production of a light source compensating element is then completed.
To achieve the object of the projecting specific light distribution (brightness distribution) onto the surface of a scanned object through light source compensating element, this invention provides the method of producing light source compensating element for scanners, comprising the following steps.
First, provide an unexposed target film and a characteristic curve; wherein the characteristic curve shows the transmittance of the target film after being exposed versus the light brightness exposing the target film.
Second, determine the required transmittance distribution on the target film in accordance with (a) a predetermined and desired brightness distribution projected onto the surface of a scanned object and (b) the brightness distribution of the scanning light projected directly onto the surface of the scanned object.
Next, expose the target film by using an even light source of adjustable brightness; wherein the brightness of the even light source is adjusted in reference with the characteristic curve, to have the required brightness for exposing the target film, thereby obtaining the required transmittance distribution on the target film.
Finally, develop the target film to form the light source compensating element.